The present invention relates to a method of lubricating a conveyor belt wherein a lubricant concentrate is employed as a dry lubricant in a dry lubrication process. The present invention further relates to the use of such lubricant concentrate as a dry lubricant, in particular for lubricating a conveyor belt.
Known conveyor belt lubricants are employed in applications in which good gliding contact between solid surfaces, for instance glass and metal, or plastic and metal must be ensured. These applications include bottle filling and conveying plants, where the lubricants are applied to the conveyor belts to ensure the trouble-free conveyance of bottles on the belt. In many known systems, a soap such as potash-based soft soap is used as the lubricant.
As a substitute for the soap-based lubricants, a variety of synthetic conveyor belt lubricants including certain amine compounds are being used. These synthetic lubricants have been described in, for example, EP-A-1690920, which discloses a lubricant concentrate containing a phosphate tri-ester. Said lubricant concentrate contains as further components an amine and an acid which may be an inorganic acid such as hydrochloric acid, nitric acid or phosphoric acid or an organic acid such as formic acid, acetic acid or oleic acid. Due to the presence of the amine, the respective lubricant does not contain the employed acid in its free form.
These conveyor belt lubricants are generally supplied as concentrates. Use concentrations (or use solutions) of such concentrates are usually prepared by applying typical dilution rates of 0.2-1.0% by weight of the respective concentrate in water depending on the friction requirement and the water type. Such aqueous belt lubricants (aqueous use solution) having a use concentrate of the active lubricating ingredients of significantly less than 0.1% by weight have been satisfactorily applied for many years. Such aqueous use solutions are also known as “wet lubricants”.
WO 01/23504 relates to such a wet lubrication process, wherein an antimicrobial lubricant composition is used to treat or lubricate containers and/or conveyor systems for containers. The employed lubricant composition comprises a lubricating agent and an antimicrobially effective amount of a quaternary phosphonium compound. The lubricant agent comprises a non-neutralized fatty acid, which may be oleic acid.
U.S. Pat. No. 6,288,012 relates to a non-aqueous lubricant for lubrication of containers and conveyor systems, whereby the substantially non-aqueous lubricant can include natural lubricants, petroleum lubricants, synthetic oils, greases and solid lubricants.
U.S. Pat. No. 4,420,578 relates to a composition for coating returnable glass bottles comprising among others 0-50 wt.-% of a fatty carboxylic acid, for example mixtures of long-chain carboxylic acids. However, said composition is employed for coating glass bottles instead of lubricating a conveyor belt.
US-A 2005/0 288 191 relates to a conveyor lubricant composition comprising at least one lubricant such as oleic acid and at least one protectant for PET bottles such as alkyl ether carboxylic acid or salts thereof.
EP-A 1 840 196 relates to a lubricant composition for conveyor systems comprising phosphoric acid esters, ether carboxylates, water and C6-C22 fatty acid, such as oleic acids, and/or C6-C22 fatty alcohols.
Kao Chemicals GmbH (Emmerich, Germany) offers a lubricant concentrate under the trade name AKYPO GENE CL 756 which contains—among others—fatty acids (approx. 10 wt.-%) and which is amine-free. Kao also suggests a method of employing said lubricant concentrate as a wet lubricant, wherein the concentrate is diluted to conveyer belt lubricants with concentrations between 8 to 11% to form an aqueous emulsion. Said diluted conveyor belt lubricant is further diluted with water to 0.2-0.4% (aqueous use solution) to be finally applied on the conveyor belt as a wet lubricant.
U.S. Pat. No. 5,723,418 relates to a lubricant concentrate composition containing an effective lubricating amount of an amine, a corrosion inhibitor and a surfactant. A fatty acid may be added to said composition as a neutralizing agent for obtaining a ph-value ranging from about 5-10.
U.S. Pat. No. 5,399,274 relates to a lubricant composition for use in metal-working processes comprising a fatty acid, an amino alcohol and a phosphate ester. The fatty acids employed are neutralized with an amino alcohol and complexed with an organic phosphate ester for obtaining a pH of the lubricant of at least about 8. The lubricant is useful in sizing, coining and machining of powdered metal parts and/or conventional ferrous and non-ferrous metal parts.
US-A 2004/0 241 309 relates to an improved food-grade lubricant useful, for example, as hydraulic oil or compressor oil. The lubricant comprises at least one vegetable oil, at least one polyalphaolefin and at least one antioxidant.
However, none of the above-described (mostly aqueous) lubricants are employed in a dry lubrication process. Most of them are employed as use solutions and therefore as wet lubricants, some of them are even used in different applications such as hydraulic oils. Most of them may contain a fatty acid such as oleic acid as an optional or even a mandatory component, but the fatty acid is usually present in its neutralized form due to additional components such as neutralizers, amines or any other components causing a pH-value in the neutral or alkaline range.
On the other hand, the application of these aqueous lubricants (wet lubricants) has also resulted in high water usage rates and relatively high effluent costs for the user. Furthermore, when used as conventionally intended these aqueous lubricants flow off the conveyor track surface treated therewith, resulting in a waste of chemical and water, and causing a slippery floor surface which may constitute a hazard to operators working in the immediate environment and collecting on floors and other surfaces which then requires cleaning.
In order to overcome the before-mentioned disadvantages of employing wet lubricants, WO 01/07544 discloses the use of a liquid composition for lubricating conveyor belts as a so-called “dry lubricant”. The liquid composition is suitable for producing a dry lubricant film which remains on the surface of the respective conveyor belt onto which it is applied (as a liquid) and which consequently does not flow off from said surface. The liquid is usually an aqueous phase (up to 95% by weight of water) and further comprises a silicone oil or other oils selected from vegetable oils, mineral oils and mixtures thereof. Vegetable oils may be soy oil, palm oil, olive oil or sunflower oil.
It is well known that such vegetable oils contain triglycerides, which are compounds formed from one molecule of glycerol (glycerine, which is a tri-hydric alcohol). Depending on the individual vegetable oil, different fatty acids are chemically bonded to glycerol. Olive oil, for example, contains triglycerides consisting of two radicals of oleic acid and one radical of palmitic acid chemically bonded to the glycerol backbone. Said vegetable oils may also contain mono- or diglycerides, having only one or two fatty acid radicals. However, said vegetable oils do not contain any free fatty acids in a significant amount. An overview of the most common vegetable oils in respect of the chemical composition can be found, for example, in the article of A. Zamora available on the internet (www.scientificpsychic.com_fitness_fattyacids). Further information can be obtained from the free internet encyclopedia Wikipedia for oleic acid (www.en.wikipedia.org/wiki/oleic_acid).
US-A 2005/0 059 564 relates to a composition and method of lubricating conveyor tracks or belts wherein the lubricant composition contains at least about 25 wt.-% of fatty acid. The lubrication process may optionally be carried out as a dry lubrication. In one embodiment, the fatty acid may be present in its free form. However, the lubricant composition requires the presence of mandatory components such as neutralizers or polyalkylene glycol polymers. Since neutralizers components such as amines or alkaline metal hydroxides are employed a rise of the respective pH-value to the alkaline range is caused. By consequence, the respective lubricant concentrate does not contain any fatty acid in its free form. A similar disclosure can be found in U.S. Pat. No. 6,427,826, U.S. Pat. No. 6,673,753 and U.S. Pat. No. 6,855,676. Nowhere within said documents describing a dry lubrication process as an optional form of lubricating a conveyor belt, a method as disclosed, wherein a lubricant concentrate containing at least one free fatty acid and at least one corrosion inhibitor is employed as dry lubricant.
One major advantage of the method of dry lubrication is the drastic reduction in the volumina of the respective liquid, which is employed for lubrication. In an ordinary dry lubrication of a conveyor belt, approximately 1.5 to 20 ml/h of the respective lubricant are applied on the conveyor belt (as dry lubricant), whereas in case of wet lubrication, approximately 10-30 l/h of an aqueous solution have to be applied on the same conveyor belt. The voluminas of the respective liquid lubricants to be employed on the conveyor belt usually differ by the factor of 1000 to 10000 (wet lubrication versus dry lubrication).
However, the method of dry lubrication as described, for example, in WO 01/07544 is also associated with some disadvantages especially due to the employment of dry lubricants containing vegetable oils, in particular mineral oils, a so-called blackening is observed on the bottom surface of the containers to be transported on the conveyor belt. This blackening is often caused by dirt usually attached to the container surface, especially in case of the transportation/re-filling of used containers or by wear of, for example, glass or metal originating from the objects to be transported on the conveyor belt. A further source of dirt on the conveyor belt are fractions of liquids such as beer or sugar-containing beverages, which have not been filled into the container during the respective (re-)filling process but have flown down on the outer surface of the respective container onto the conveyor belt. The blackening problem usually occurs only in the case of a dry lubrication process, but not during a wet lubrication process.
Since it is difficult to remove said mixture of dirt and vegetable oil or especially mineral oil from the conveyor belt to avoid blackening, the whole conveyor belt system has to be stopped from time to time to perform an additional cleaning step. This cleaning is usually performed by employing strong alkaline detergent compositions containing surfactants because the oil-dirt-mixtures especially when employing mineral oils, can only be insufficiently removed by ordinary aqueous detergent compositions. If the used up lubricant film is not completely removed from the conveyor belt, the blackening problem is not solved. In addition, the new lubricant film is formed incompletely causing problems in respect of the objects to be transported. After the cleaning, further time has to be spent to sufficiently (re-) to apply the lubricant on the respective conveyor belt (so-called starting phase) until the whole system can be operated without any problems in respect of the transportation of the containers.
Therefore, the object of the present invention is to provide a new method of dry lubrication for a conveyor belt.
The object is achieved by a method of lubricating a conveyor belt, wherein a lubricant concentrate containing at least 0.1 wt.-% of at least one free fatty acid and at least one corrosion inhibitor, is employed as a dry lubricant in a dry lubrication process.